Improved initial conditions of the electron ionized by a strong, linearly polarized laser field and their reconstruction from the detected momentum of the electron

Tunneling time and exit momentum are of outstanding importance regarding both quantum theory and attosecond metrology. Several research groups published relevant experimental results, and the explanatory theoretical models often employ classical dynamics, where the choice of proper initial conditions is an important open question.

We focus on atomic hydrogen driven by a linearly polarized few-cycle near-infrared laser pulse having a peak intensity that ensures tunneling. We show the real classical picture associated with the exact quantum process of strong-field ionization in the parameter range relevant to state-of-the-art experimental techniques [Sz. Hack et al. Phys. Rev. A, 104, L031102 (2021)]. This classical model follows the quantum evolution very well; it accounts for direct ionization, rescattering and the blurred nature of the liberation process; it solves and explains the problem of the non-zero initial momentum in models assuming traditional tunneling.

Using the improved initial conditions, we show a simple procedure to reconstruct the starting time from the detected momentum of a directly escaping electron. We tested this method with numerical experiments resulting the accuracy of the reconstructed starting time less than 5 as for the most probable trajectories.